1. Field of the Invention
The present invention relates to a positionally- or location-sensitive proportional geiger or counter tube of high resolution with a counting chamber which is lined with a trough-shaped metallic layer introduced in or vapor-deposited on an insulating body as a cathode, which is gas-tightly covered on its longitudinal side through the intermediary of a conductive and radiation-transmissive foil as a counter tube window, and traversed along its longitudinal direction by a counter tube wire forming an anode and which is maintained stretched equidistantly from the metallic side trough walls, and which is fastened at both sides thereof in the insulating body and connected with the electrical elements of amplifiers.
2. Discussion of the Prior Art
Heretofore, for the registration of X-ray diffraction diagrams it has been the common practice to employ a photographic film. However, a darkened photographic film is subject to a relatively high "background noise" and, within its narrow linear range, to a "dynamic range" of only 1:10. As a result, for spectra having a strongly fluctuating intensity distribution a plurality of exposures must be taken with, at least partly, extremely lengthy exposure periods.
As an alternative to the photographic film there are presently offered two measuring methods employing counter tubes for the registration of X-ray diffraction diagrams. The first method is based on the principle that the surface which is to be measured is scanned through the intermediary of a detector and the activity at the current measuring location is registered over a predetermined time interval. In this manner there can be achieved a good positional or localized resolution capacity, however, only under the assumption that, during the entire duration of measurement, there is no change in the diffraction characteristics of the preparation which produces the X-ray spectrum. Moreover, no intensity fluctuations may occur in the X-ray light source. Consequently, discussed hereby is a timewise short resolution capacity for this measuring method.
The second method operates with a number of detectors, which concurrently measure the intensity distribution for a predetermined area of the registration plane. However, the advantage of the good timewise resolution must be bought in conjunction with a deterioration in the positional or localized resolution, which is restricted through the measurements of the individual detectors. Furthermore, an added disadvantage herein lies in the great complexity of the apparatus.
Recently, attempts have been made to develop detectors which not only register the particles (quantum), but which will concurrently provide information with respect to the measured location. The efforts were exerted in a direction to make the positional or localized resolution of these detectors as good as possible, so as to be able to compete with the resolution of the film. In actual use, such a detector would be superior to a film since the dynamic range of a detector is considerably better than that of a film, namely, by a factor of 10.sup.3. In addition thereto, a measured spectrum is immediately present in the form of data acceptable to a computer whereas, in contrast therewith, a film must be first developed and thereafter the intensity distribution must be determined photometrically. Moreover, at a good efficiency of the detectors one can hope to obtain a reduction in the measuring time.
It has also been attempted to find a compromise of the two above-mentioned methods, in which a plurality of counter tubes were arranged as detectors in the measuring plane. Each individual one of these counter tubes delivers a positional information along its counter tube wire in which the final time duration of the discharge, which proceeds from the location of the primary avalanche to the wire ends, is employed as the measure for the location of the irradiation. Also refined evaluation techniques, for instance, through quotient formulation of the impluses obtained at both sides of the ends of a counter tube wire of a proportional counter tube, still did not bring an adequate positional or localized resolution.
With the measurement of impulse rise time periods which depend upon the location of an ionizing X-ray quantum received on a high-ohmic counter tube wire of a proportional counter tube, there could be achieved a decisive improvement in the resolution. In this method there is employed a proportional counter tube with a high-ohmic counter tube wire which, together with the counter tube capacitance, represents a continuous low-pass. The charge on the wire location, which corresponds to the irradiation or incident beam location of the ionizing X-ray quantum, flows out over this continuous low-pass and generates a current impulse at the input capacitance of the preamplifier of the counter tube. The rise period of this impulse is dependent upon the length of the continuous low-pass through which there must flow the charge from the irradiation location to the counter tube end. In a counter tube of this type which has become known, the positional information is derived from impulses tapped off at both of the counter tube wire ends, which are initiated by an ionizing phenomenon, whereby the difference between the impulse rise time periods is a direct measure for the irradiation location. Thus, by means of a known counter tube having the above-mentioned construction being operated pursuant to this method, with an effective length of about 55 mm under the application of a collimated X-ray beam with a diameter of less than 100 .mu.m, there can be achieved a local or positional resolution of 160 .mu.m (half-value width of the positional signal).
This positional resolution of the counter tube can only be reached under normal pressure through the utilization of the extremely expensive xenon as the counter tube gas. On the other hand, a closed counter tube, which only reuires a single gas filling, is problematic since such a closed counter tube must be highly vacuum-tightly sealed and, prior to being filled with the counter tube gas, must be heated in a vacuum. However, the counter tube wire is pulled apart by the given expansion of the counter tube body due to its extrmemely low mechanical load capacity (carbon-coated quartz wire having a diameter of 24.5 .mu.m). It is difficult to formulate a suitable clamping arrangement for the counter tube wire. Hereby, care must be exercised that no change in the capacitance is produced at the wire end, since these will have a disruptive effect on the counter tube impulses which are to be evaluated.